Phil! Gold :: 30 Oct 2017

Mon, 30 Oct 2017

How to Buy Batteries for Flashlights

Questions about buying batteries come up periodically on the
/r/flashlight subreddit. This is the guide I wish had existed when I
had those questions. The primary focus of this guide is on batteries that
go into flashlights, though some of what's here can certainly be applied
to other battery-powered devices.

If you just want to know how to get 18650 batteries, skip down to the
Lithium-Ion section. Be careful when buying lithium-ion
batteries from marketplaces like Amazon; unsafe batteries abound. See the
section for advice on making safe purchases.

Types of Batteries

Batteries can be separated into different types that largely have to do
with their voltage. A battery's voltage is determined by the chemical
reactions it uses to generate electricity (and occasionally with
additional circuitry added to the battery). The usual way we refer to
batteries (AA, AAA, C, etc.) specifically references their size, not
voltage. Fortunately, for the most part, particular sizes only come in
particular voltages. I'll note a few places you might have to take care.

Flashlight batteries generally fall into one of three categories (links go
to the sections on each type of battery):

1.5V - These include the most common battery types in use,
including AAA, AA, C, and D.

3V - The most common 3V flashlight battery is the
CR123A. Many button cells (watch batteries) are also 3V, like the
common CR2032.

Lithium-Ion - This is a whole class of batteries that have
higher outputs and last longer than many other flashlight batteries,
but they require more care in handling. Lithium-ion flashlight
batteries usually have five-digit designations, like 18650 and 10440.

I'm omitting stuff like 9V batteries and 6V "lantern batteries", since
they're not used in flashlights to the same degree that the above
categories are.

1.5V Batteries (AA, C, etc.)

Flashlights that use AAA, AA, C, and D cells are very common. They're
useful because those cells are also very common.

People sometimes refer to these batteries as either "primaries" or, less
often, "secondaries". "Primaries" are synonymous with non-rechargeable;
you use them and then throw them away. "Secondaries" are synonymous with
rechargeable, though people will more often just call them "rechargeable".

The main consideration when choosing 1.5V batteries is the chemistry used
inside. There are three common chemistries:

Alkaline - The cheapest and most common. Not recommended unless
they're your only option. They're not rechargeable, so you have to
replace them every time you use them up. They lose their charge over
time, so if you leave them alone for a while, they might not even be
useful when you do pick them up. They tend to leak, which becomes more
likely the more they discharge (and remember, they lose charge even if
you're not using them). When they leak, they can destroy whatever
device they're in.

Nickel-metal Hydride (NiMH) - Rechargeable. People will often refer to
"Eneloops", a specific, well-regarded brand of NiMH batteries. Good
for frequently-used flashlights because you can reuse them rather than
buying new ones all the time. They also don't leak, so you don't run
the risk of damaging your devices. Standard NiMH batteries lose charge
much faster than alkaline batteries, but you can get "low self
discharge" NiMH batteries that only lose their charge slightly faster
than alkalines do. (Rough comparison: after a year without use or
charging, an alkaline battery will have 80-90% of its original charge,
an LSD NiMH will have 70-80%, and a regular NiMH will have 15-20%.)
Although alkalines usually claim more energy storage than NiMH on
paper, NiMH batteries tend to give longer runtimes in flashlights in
practice because of the way modern flashlights use electricity.

Lithium - Expensive, but long-lasting. Not rechargeable. These
typically cost three times or more what alkalines do. (So do NiMH
batteries, but those are rechargeable, so the cost is amortized over
many reuses.) They lose their charge more slowly than alkalines, they
can store more energy than alkalines or NiMH, and they don't leak.
Good for devices you want to leave alone for months or years at a time
and still work as soon as you pick them up again.

There are rechargeable alkaline and rechargeable lithium batteries, but
rechargeable NiMH are the most common at the moment. Nickel-cadmium (NiCd)
used to be the most common rechargeable chemistry, but it's been replaced
by the NiMH, which is better than NiCd in practically every way.

In most cases, you should get NiMH rechargeable batteries for flashlights
that get used frequently. For flashlights that sit and wait to be used
(emergency flashlights, bug out bags, etc.), use lithium primaries.

Lithium batteries handle temperature extremes better than NiMH and
alkaline batteries, so lithium is also the best choice for things like
flashlights that live in cars.

3V Batteries (CR123A, etc.)

3V batteries are common in a number of more niche devices, like cameras.
There are a lot of flashlights that use 3V CR123A batteries. Pretty much
every 3V battery uses lithium, so everything about lithium in the
1.5V section applies to 3V batteries, too.

The higher voltage lets some CR123A flashlights put out more light than
similarly-sized AA flashlights. Aside from that, there's not much to
consider about buying CR123A batteries.

Some places sell "RCR123A" batteries, which are basically CR123A-sized
lithium-ion batteries. (Specifically, they're 16340 cells; lithium-ion
naming conventions are covered below.) Some RCR123A batteries have
integrated voltage-regulating circuitry to deliver a constant 3V so they
behave just like a regular CR123A. Others do not; like other lithium-ion
batteries, they'll be 4.2V when fully charged. If you're going to buy
RCR123A batteries, either make sure your device can handle voltage up
to 4.2V or check the specs on the RCR123A to see whether it has a 3V
output. (Lithium-ion batteries will often be listed as having a 3.6V
output or so.)

Lithium-Ion Batteries

Lithium-ion batteries brought a revolution in compact energy storage.
They can hold more energy and discharge it faster than any of the common
handheld battery technologies that came before them. Lithium-ion
batteries are used, in some form, in devices ranging from smartphones to
laptops to electric cars.

Lithium-ion batteries supply 4.2V when fully charged. As their energy is
drained, their voltage drops. When they reach 2.5V or so, they're
considered empty. Although a lithium-ion battery can continue to supply
power beyond that point, doing so will permanently damage the battery's
chemistry. That might reduce the energy the battery can hold when full,
render the battery useless, or cause an internal short circuit that could
lead to a fire.

Lithium-ion batteries are also potentially more dangerous than the other
batteries described above. If they get too hot, they can catch fire or
explode. Charging and discharging lithium-ion batteries both generate
heat, so doing either one too fast can cause a fire or explosion. A short
circuit--connecting the positive and negative ends without enough
resistance in between--will almost certainly discharge the battery too
rapidly. (For people who remember the Samsung Galaxy Note 7 fires, those
were caused by unsafe lithium-ion batteries.)

The above doesn't need to put you completely off lithium-ion batteries.
They're incredibly useful; you just need to take a little more care with
them than other common batteries. Some lithium-ion batteries are more
safe than others; that'll be covered below.

You do need to be careful about where you buy your lithium-ion batteries.
Many large marketplaces, like Amazon and AliExpress, have unsafe or
mislabeled lithium-ion batteries for sale. Because of the dangers of
unsafe usage of such batteries, you need to make sure you're getting them
from a reputable seller. That will be covered in the
buying lithium-ion batteries section.

Some flashlights have built-in charging circuits. If yours doesn't,
you'll also need a charger, covered in the chargers section.

Lithium-Ion Names and Shapes

The Lithium-ion batteries that flashlights use--at least, flashlights with
removable batteries--are generally cylindrical and are described by a
five-digit identifier, like "18650". The first two digits give the
diameter of the cylinder in millimeters (mm). The last three digits give
the length of the cylinder in tenths of a millimeter. Thus, an 18650 cell
is nominally 18mm by 65mm. There's some variation in those values,
particularly in the length, but they give a rough approximation.

Some common sizes are:

18650 - The most ubiquitous size for lithium-ion flashlights, as well
as for a lot of other things (laptop batteries, smartphone power banks,
and so on). Because this is currently one of the most popular sizes in
industrial use, it's gotten the most research into making it
efficient. As of January 2018, no other shape matches the energy
density of the 18650. (e.g. a 26650 has twice the volume of a 18650,
but the best 26650 only has 1.5 times the energy of the best 18650.)

26650 - The 18650's larger sibling. Used by some flashlights to give
more runtime per battery.

18350 - Almost half the size of an 18650. A number of flashlights have
options for swappable longer and shorter battery compartments, so you
can decide on a daily basis whether to have a shorter light that uses
18350s or a longer light (with longer runtimes) that uses 18650s.

16340 - More or less the same size as a CR123A. There are used in
"RCR123A" batteries as described in the 3V section
above.

14500 - More or less the same size as a AA battery. Some flashlights
can use either AA or 14500 cells. Don't use a 14500 battery in a AA
light unless the flashlight manual says you can. If the flashlight
only expects 1.5V batteries, using a 4.2V 14500 can destroy the light
and possibly start a fire.

10440 - More or less the same size as a AAA battery. Some flashlights
can use either AAA or 10440 cells. Don't use a 10440 battery in a AAA
light unless the flashlight manual says you can. If the flashlight
only expects 1.5V batteries, using a 4.2V 10440 can destroy the light
and possibly start a fire.

A number of flashlights allow you to use either an 18650 battery or two
CR123A batteries. As with 14500/AA and 10440/AAA, don't do this unless
the flashlight manual says you can, since two CR123A batteries in series
will give the flashlight 6V.

When speaking, most people break up the five digits of a lithium-ion
battery into three groups: xx-y-zz. Thus, "18650" is pronounced
"eighteen-six-fifty". ("14500" is usually pronounced
"fourteen-five-hundred".)

What You Need to Know About Lithium-Ion Options

With 1.5V batteries, you have just one thing to decide about: the battery
chemistry. With lithium-ion batteries, there are four options you need to
consider: protection, top shape, capacity, and discharge rate.

If in doubt, you'll probably be okay with protected, button-top batteries
of the highest capacity you can afford (ignoring discharge rate).

Protection

Dimensions of plain, button-top, and protected 18650s.

As noted above, lithium-ion batteries should not be discharged below 2.5V
or so and should not be discharged too quickly. Many manufacturers take
plain lithium-ion cells and add small protection circuits on top. These
circuits stop providing power if the battery voltage drops too low or if
the current draw gets too high, protecting the cell from things that could
damage it. This makes the protected batteries a bit safer, since it's
more difficult to accidentally push them too hard.

A protection circuit makes the battery a little longer, and sometimes a
little wider. There are flashlights that have so little extra space
inside that they must be used with unprotected batteries. Usually such
flashlights will have their own low-voltage protection (LVP) and will stop
trying to use the battery if the voltage gets too low. If you use an
unprotected battery in a flashlight without LVP, you'll have to be careful
not to drain the battery too far or you risk permanently damaging the
battery.

Protected batteries usually cost a little bit more than their unprotected
counterparts, typically in the realm of an extra $1.50 or so.

Some high-powered flashlights need to draw so much current that they can't
use protected batteries because they'd trip the protection with their
power usage. For those flashlights, make sure you get unprotected
batteries with a high enough discharge rate (covered later).

Flashlights that need unprotected batteries should say so on their website
and in their manual. If there's nothing about protection, you should be
able to use protected batteries (and you ought to do so).

Top Shape

Tops and bottoms of flat top, button top, and protected 18650s.

Lithium-ion batteries, like all other batteries, have a positive end and a
negative end. Putting a lithium-ion battery in backwards can damage the
flashlight, the battery, or both. In some cases, it can start a fire.

On a plain cylindrical lithium-ion cell, the disk on the positive end is a
little smaller than the disk on the negative end. Some manufacturers take
bare cells and put buttons on top of them, like the buttons on top of 1.5V
batteries. This makes the battery a little longer, but not as much as a
protection circuit does. Most unprotected-batteries-only flashlights will
still work with button top batteries.

Button top batteries usually cost slightly more than flat top batteries.
The extra cost is generally somewhere around ten to twenty cents.

Many flashlights will work with either button top or flat top batteries.
Some are shaped so that only a correctly-inserted button top battery will
work. This serves as mechanical enforcement of correct battery polarity.
If your flashlight takes more than one battery in series, you'll need to
use button-top batteries.

Protected batteries pretty much always come with button tops.

In general, any flashlight that works with flat tops will also work with
button tops, except for rare cases where the battery compartment spacing
is incredibly tight. Consequently, I'd recommend getting button top
batteries unless you specifically know you need flat tops.

Capacity

A battery's capacity, most commonly measured in milliamp-hours (mAh),
governs how long it can continue providing power. More mAh generally
equals more flashlight runtime. Even if you don't expect to run a battery
all the way down, keep in mind that as a lithium-ion battery discharges
its voltage drops. In many flashlights, that means that a
partially-discharged battery can't support the brightest modes on the
light. A higher-capacity battery will continue to provide higher voltages
for longer periods of time.

If all else is equal, you should get the highest-capacity battery you want
to spend money on.

Many disreputable battery vendors claim impossibly high capacities for
their batteries. As of January 2018, here are the highest manufacturered
capacities for some common lithium-ion sizes; if a battery claims
significantly higher numbers, it's probably lying (and if it's lying about
capacity, it's a lot more likely to be lying about other things, like
safety):

16340 - 700mAh (see the note below about Efest)

18350 - 1200mAh

18650 - 3600mAh (but see the note below)

26650 - 5500mAh

(Note: Efest, a reasonably reputable brand, sells "850mAh" 16340s, but
testing indicates that they're more than a little optimistic about that
claimed capacity. In practice, 700mAh is the most you'll get out of
a 16340.)

(Note: Only one 18650 cell claims a 3600mAh capacity, and it's arguably
cheating a little to get that number. For most practical purposes, you
can regard 3500mAh as the highest available 18650 capacity, and consider
any "3600mAh" battery to really be 3500mAh.)

Discharge Rate

Depending on their particular chemistry, lithium-ion batteries can have a
maximum discharge rate anywhere from 3 amps (A) to 40A. Most flashlights
stay under 3A-4A, so pretty much any battery will be fine for them. Some
of the higher-output flashlights need or can benefit from 10A, 15A, or
even 20A batteries.

There's a tradeoff between battery capacity and discharge. The
chemistries that do very well on one metric are not as good on the other.
As of January 2018, the best high-capacity batteries store 3500mAh with a
maximum discharge of 10A, while the highest-discharge batteries can
sustain 40A but only store 2000mAh.

The most-demanding flashlights I've seen top out at about 20A, so you
probably don't need to go out looking for batteries with higher discharge
rates than that. (Unless you're also using the batteries in your vape or
something.) Many people with high-drain flashlights like to use Sony VTC6
or Samsung 30Q batteries; both are 3000mAh/15A.

Some people refer to high-discharge batteries as "IMR" batteries, after a
commonly-used chemistry for such batteries.

In general, you should see if your flashlight has a maximum current drain
listed. If it doesn't, ignore discharge rate and get the highest capacity
batteries you want. Otherwise, get the highest-capacity batteries with a
high enough maximum discharge rate.

Other Considerations

There are all sorts of other characteristics that people care about with
their batteries, but those are less relevant than the above four things,
especially if all you care about is getting your flashlight to work.

There's actually a really complex relationship between batteries'
capacity, voltage, and current. Batteries are a little less efficient at
higher amperages, so a flashlight that's constantly used on its turbo
setting will generally drain its battery even faster than the numerical
difference between the light's brightness levels would indicate.
Similarly, batteries providing higher amperages will have their voltage
drop a bit relative to the same battery with the same charge but at a
lower current draw. Different batteries will have different balances
among those relationships (e.g. Samsung 30Qs exhibit slightly more voltage
sag than Sony VTC6s, even though their top-line ratings are the same).

These sorts of things only tend to matter to people who want to squeeze
every last lumen out of their lights, and those are just a small subset of
the people who use lithium-ion flashlights on a regular basis. If you're
interested in this level of detail, though, you will want to look at
HKJ's battery and charger reviews. The website is a little
confusing in its layout, but there's a wealth of information about all of
the batteries HKJ has tested, and HKJ has tested a lot of batteries.

Where to Buy Lithium-Ion Flashlight Batteries

Don't just go to Amazon, search for "18650", and buy the first search
result. There are a lot of cheaply-made and more-unsafe-than-necessary
batteries in large marketplaces like Amazon. You should buy from a vendor
who will only sell properly-labeled stock from trusted manufacturers.

One of the easiest ways to do that, as well as to search for batteries
that match all of the options you need, is to use the
Parametrek Battery Database. The person who
maintains the database has links to purchase batteries from reputable
sellers. For a search example, here's all of the protected 18650
batteries, with the highest-capacity ones first:

Note that to search for capacity, the mAh numbers I've talked about are on
the "mAh" category. The "capacity" section sorts by watt-hours (Wh)
instead. (The basic difference is that milliamp-hours are only directly
comparable for batteries at the same voltage, while watt-hours give
meaningful comparisons even between batteries with differing voltages.
Lithium-ion batteries are generally marketed with their mAh rating--since
the voltage is known--so that's what this guide uses, too.)

If you have questions about a particular battery seller, you can always
come ask about it on the /r/flashlight subreddit.

Notes on Particular Lithium-Ion Battery Brands

Unprotected batteries are pretty much all made by LG, Panasonic,
Samsung, Sanyo, or Sony.

Some of the more popular brands for protected batteries include AW,
EVVA, and Keeppower.
(As mentioned previously, these companies buy
unprotected batteries from the above vendors, add their own protection
circuits, and sell the resulting batteries.)

Many flashlight manufacturers have their own branded batteries. Those are
generally of good quality, but they're often more expensive than
equally-good batteries from other reputable sellers. Some people prefer
to pay the extra amount just to avoid trying to figure out whether a
particular other seller is reputable or not.

Batteries from Olight are a little unusual. They're a reputable
manufacturer (and seller, if you buy directly from them), but they do some
extra things to their batteries. The tops of their batteries have a
positive button, like any button top battery, but also a negative ring
around the button. This is required for the batteries to work in their
proprietary flashlight charging cradles, but it increases the chances of
short-circuiting the batteries. (The protection circuit should prevent a
short-circuit from starting a fire, but it's still not something you want
to do to a battery.) Unless you're using an Olight flashlight with an
Olight charger, you probably don't want an Olight battery.

Ultrafire batteries should be avoided. They're known to cut corners
on their batteries in order to make them cheaper. If you buy one of their
batteries, you might get something that works, but you also might get a
battery with a defective protection circuit, or a battery that contains a
smaller, cheaper battery, and a lot of sand to fill the extra space.
Given the care that needs to be taken with lithium-ion batteries, the risk
isn't worth the lower prices.

Chargers

If you go with rechargable batteries, you'll need a charger. (Some
lithium-ion flashlights have built-in charging, but even with those an
external charger can be useful sometimes.)

The best option is to look at the list of
chargers reviewed by HJK, pick one with the features you
need (number of bays, NiMH, lithium-ion, etc.) and a good rating (two or
more smiling faces), and buy it from one of the reputable battery vendors
discussed above.